linux-kernel - Re: VM issue causing high CPU loads

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Date:	Thu, 03 Sep 2009 16:49:25 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Simon Kirby <sim@...tway.ca>
Cc:	Yohan <ytordjman@...p.free.fr>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	Neil Brown <neilb@...e.de>,
	"J. Bruce Fields" <bfields@...ldses.org>, mikevs@...all.net
Subject: Re: VM issue causing high CPU loads

On Thu, 2009-09-03 at 13:05 -0700, Simon Kirby wrote:
> On Thu, Sep 03, 2009 at 10:02:06AM -0400, Trond Myklebust wrote:
> 
> > OK, so 16 hash buckets are likely to be filled with ~10^6 entries each.
> > I can see that might be a performance issue...
> 
> We have a similar setup with millions of UIDs over NFS (currently NFSv3).
> I _wish_ there were a way to use NFSv4 without having to use name-mapped
> UIDs and GIDs, since our user and group names come from MySQL anyway, and
> are guaranteed to be consistent across machines.

That's a separate issue.

I'm working on increasing the idmapper scalability, however another
project is currently taking up most of my time. I can't guarantee that
the revised idmapper code will be finished in time to allow for
inclusion in 2.6.32.

> Why on earth does NFSv4 force the use of names?

NFSv4 aspires to be an internet-wide protocol, and so you cannot use
uids/gids: they just aren't guaranteed to represent a unique user
outside your local LDAP/NIS or /etc/passwd domain. Furthermore, uids and
gids are a posix construct. They simply don't work in environments where
you may have lots of non-posix systems.

Trond

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